1. Field of the Invention
The present invention relates to an image defect detection device and an image defect detection method which detect image defect, and an imaging unit for image defect detection.
2. Description of the Related Art
A single-pass ink jet recording apparatus which forms an image on a recording medium by ejecting ink droplets from a plurality of ink ejection nozzles (hereinafter, simply referred to as nozzles) provided in an ink jet head while relatively moving the recording medium and the ink jet head has been known.
In the ink jet recording apparatus, a failure nozzle, such as a non-ejection nozzle which cannot eject ink droplets due to clogging or breakdown over time or a deflected nozzle in which the amount of flight deflection of ink droplets is increased, is generated. In this case, in the single-pass ink jet recording apparatus, stripe unevenness (white stripe or white-black stripe) of a shape extended in a transport direction of the recording medium (or a moving direction of the ink jet head) occurs in a recorded image. In addition, scratches extended in the transport direction occur in the recorded image due to contact between a recording surface of the recording medium and a member constituting a transport system of the recording medium. For this reason, an ink jet recording apparatus which has a function of detecting image defect, such as stripe unevenness or scratches, is well known.
For example, JP2006-240000A describes an ink jet recording apparatus which detects image defect using an imaging unit provided with an optical sensor having a plurality of read pixels disposed on a plane and an image forming optical system. In an image defect detection device, a sensor light receiving surface of the optical sensor and a principal plane of a lens are inclined with respect to the recording surface of the recording medium which is a surface of an object to be measured. With this, even when the distance between the imaging unit and the recording surface of the recording medium is changed, an image of the recording surface is focused on any place on the sensor light receiving surface. Therefore, it is possible to obtain a signal of a focused image. As a result, it is possible to detect image defect.